1. Field of the Invention
This invention relates to an apparatus and method for removing fluid from a fibrous web. More particularly, this invention relates to an apparatus and method in which a formed web is subjected for an extended period to increased pressure and temperature such that fluid within the web is removed.
2. Information Disclosure Statement
In the papermaking art, as much water as possible is removed from the formed web in the press section because mechanical removal of fluid at this stage is more economical than subsequent removal of fluid in the drying section of the papermaking machine.
In U.S. Pat. No. 4,738,752, a so-called "high temperature pressing apparatus and method" is disclosed in which the paper web is subjected to a press drying operation for removing most of the water from the fibrous web. The high temperature pressing technique involves the application of high temperatures and pressure to the paper web for an extended period of time. In one embodiment of the high temperature pressing (HTP) process, the web to be dried extends through a press which includes an elongate shoe and a cooperating backing roll. A blanket extends, together with the web, through a pressing section defined between the shoe and the backing roll (or pressing member). The pressing member is inductively, or otherwise, heated such that during passage of the web through the pressing section, fluid within the web is vaporized to force fluid remaining in the liquid phase away from the web.
Because of the very high temperature employed in the aforementioned HTP process coupled with the extremely high pressures, delamination of the formed web has been experienced. Such delamination occurs primarily as the result of the rapid evolution of vapor within the pressing section with such vapor blowing the web apart as the web exits from the pressing section.
The present invention seeks to overcome the aforementioned problem by providing the press member (or backing roll) with a porous layer such that the high pressure vapor within the pressing section diffuses into the porous layer. Additionally, the porous layer tends to reduce thermal transfer between the press member and the web which further inhibits delamination of the pressed web.
Therefore, it is a primary objective of the present invention to overcome the aforementioned problems associated with the aforementioned press drying apparatus and techniques and to provide an apparatus and method which contributes significantly to the press drying art.
Another object of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the press member defines a pressing surface which is porous.
Another object of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the press member includes a first and a second coaxial layer with the second coaxial layer extending around the first layer, the second layer defining a cylindrical pressing surface.
Another object of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the second layer is sintered and has a pore size of at least 2 microns.
Another object of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the second layer has a thickness of at least 0.005 inches.
Another object of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the sintered layer is spray-coated onto the first layer which is a backing roll of an extended nip press.
Another object of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which a fiber metal felt is disposed between the press member and the web such that in operation of the apparatus, the metal felt passes with the web through the press section and in which the metal felt is heated immediately prior to the passage of the felt through the pressing section.
Another object of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which a cleaning means is provided for passing a cleaning medium through the metal felt towards a surface of the metal felt contacting the web so that contaminants picked up by the metal felt during operation of the apparatus are ejected from the metal felt.
Another object of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the first layer of the press member is vented.
Other objects and advantages of the present invention will be apparent to those skilled in the art by consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.